The potential value of autostereoscopic display systems is widely appreciated particularly in entertainment and simulation fields. Autostereoscopic display systems include “immersion” systems, intended to provide a realistic viewing experience for an observer by visually surrounding the observer with a three-dimensional (3-D) image having a very wide field of view. As differentiated from the larger group of stereoscopic displays that include it, the autostereoscopic display is characterized by the absence of any requirement for a wearable item of any type, such as goggles, headgear, or special glasses, for example. That is, an autostereoscopic display attempts to provide “natural” viewing conditions for an observer.
One example autostereoscopic system is disclosed in commonly-assigned U.S. Pat. No. 6,416,181 (Kessler et al.), incorporated herein by reference, herein referred to as the '181 patent. In an autostereoscopic projection apparatus 10 as described in the '181 disclosure and as shown in FIG. 1, a curved mirror 24 is employed, in combination with a beamsplitter 16 for providing an autostereoscopic virtual image to a viewer 12 at left and right viewing pupils 14l and 14r. For left and right viewing pupil 14l and 14r, a corresponding image generation system 70l and 70r provides an initial intermediate curved image that is then projected through a ball lens segment 30 in order to form a left or right intermediate curved image 80l or 80r at a focal plane of curved mirror 24.
The substantially monocentric optical apparatus of the '181 disclosure provides realistic autostereoscopic imaging with large viewing pupils, a very wide field of view, and minimal aberration. However, one salient limitation of the apparatus represented in FIG. 1 is its constraint to use by only one viewer 12 at a time. While this arrangement may be suitable for some types of simulator or entertainment applications, there can be applications where it is advantageous, and more cost-effective, to provide autostereoscopic images to a second viewer 12.
Aultostereoscopic display systems for multiple viewers have been proposed, including the following:                U.S. Pat. No. 6,449,090 (Omar et al.) discloses a dual-function apparatus that can be used to provide an autostereoscopic image to a single viewer and stereoscopic images to multiple viewers, each of whom, however, requires a polarizing or shuttering device; and        European Patent Specification EP 0 602 934 discloses an autostereoscopic display apparatus that provides a real image simultaneously to two observers. One shortcoming of this approach for many types of display applications relates to the separation of left- and right-eye images; in a disclosed embodiment, right- and left-eye images are reversed for the two observers.        
For fully satisfactory 3-D viewing, an autostereoscopic display system should provide separate, high-resolution images to right and left eyes. It can also be readily appreciated that such a system is most favorably designed for compactness, creating an illusion of depth and width of field, while occupying as little actual floor space and volume as is possible. For the most realistic viewing experience, the observer should be presented with a virtual image, disposed to appear a large distance away. Thus, it can be seen that there is a need for an autostereoscopic imaging subsystem using pupil imaging that provides virtual images for multiple viewers.